Friendship problem

I have this friend who I’ve known for over 10 years and our parents are really close etc. I understand she is busy, and we go to different schools so I don’t expect her to think of me too much. I’m upset because I’m the one who always has to initiate things, or when she does, it’s because her mum suggested to meet me. So for a while, I just stopped asking to hang out because I was busy, and she always makes up excuses, like “I’m tired” or “let’s just go next week” over and over again. And i see her instagram story where she is literally with another friend, so I just assumed she must not like me anymore or something.
I think she’s also ‘using’ me(?) to get things she wants, because she invited me to a concert to go with her, and i said yes because at the time we were somewhat closer. I later found out that she has another friend she plans to go with, and only invited me because her mum wouldn’t buy the tickets unless she went with someone her mum knew (aka me). And she didn’t even tell me about her friend, I found out from her mum randomly a few weeks later. I want to go to the concert, but I really don't want to be that awkward person standing around them, and plus the tickets were expensive so I’m regretting it. I’m not sure if I should go because I also don’t know her friend at all. what should I do?